An important aspect of using semiconductor chips is removing heat generated by the chips during use. If a chip is bonded to a circuit board, the heat generated by the chip can be transferred to the circuit board. To maximize such heat transfer, the circuit board should be made of a material having high thermal conductivity. A preferred material for the circuit board is diamond, which has the highest thermal conductivity of any material. Diamond unfortunately has a coefficient of thermal expansion that is substantially different from that of typical chip material like silicon or gallium arsenide; diamond has a thermal expansion coefficient of 0.8 parts per million/K, while silicon and gallium arsenide have coefficients of thermal expansion of three and seven parts per million/K, respectively.
If an elevated temperature process such as soldering is used to bond a semiconductor chip to a diamond circuit board, the chip will have high tensile stresses after the chip and the circuit board have cooled to room temperature due to the thermal expansion mismatch between the chip and the circuit board. These stresses may cause the chip to crack. Additionally, thermal cycling during the soldering process or during use of the chip may lead to a failure of the bond between the chip and the circuit board.
A need has thus arisen for a chip mount or a method of mounting a chip on a circuit board that reduces stresses caused by thermal expansion mismatch between the chip and the circuit board.